An airbag system for protecting occupants in the event of a frontal collision is installed in conventional vehicles. The airbag system is configured to deploy an airbag to a vehicle compartment when a collision detection sensor set in a vehicle front detects a collision. Various proposals have been made about a position where to set the collision detection sensor because the position is important in detecting a collision of a vehicle in a short time to deploy the airbag quickly.
For example, Patent Literature 1 discloses an invention in which the collision detection sensor is set on a connection member for connecting a radiator shroud upper extending in a vehicle width direction, and a bumper reinforcement arranged obliquely frontward and downward from the radiator shroud upper. According to the invention disclosed in Patent Literature 1, in the event of a frontal collision of the vehicle, the collision detection sensor is capable of detecting the collision of the vehicle because the connection member is deformed toward a vehicle rear to move the collision detection sensor toward the vehicle rear.
The connection member of Patent Literature 1, however, may not be easily deformed in the event of a frontal collision of the vehicle, because the connection member is formed of a single member having a U-shape in a cross-sectional view and relative high rigidity. This inhibits an amount of movement toward the vehicle rear of the collision detection sensor set on the connection member. There is still room for improvement in quick collision detection. Specifically, the more easily a member on which to set the collision detection sensor is deformed, the more easily the sensor moves rearward to detect the collision more quickly. For this reason, the member on which to set the sensor needs to have deformability (low rigidity).
For the purpose of satisfying such need, Patent Literature 2 discloses an invention in which: left and right vertical frame parts forming a front bulkhead having a rectangular shape in a front view are made from panel material; and the collision detection sensor is set on the vertical frame parts. According to the invention disclosed in Patent Literature 2, since the vertical frame parts are formed from the panel material and their rigidity is relatively low, the vertical frame parts are easily deformed, and quick collision detection can be realized.
In a small overlap collision in which a collision object such as an oncoming vehicle collides at a position outward of a front side frame in the vehicle width direction, there is a case where a power unit including an engine and a transmission moves toward the vehicle front to hit a lower lateral frame part included in the front bulkhead. In this case, the rigidity of the vertical frame parts connected to the lower lateral frame part needs to be increased in order to support frontward load applied to the lateral frame part. In other words, the vertical frame parts need to have shape retainability (high rigidity).